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United States Patent |
6,083,403
|
Tang
,   et al.
|
July 4, 2000
|
Stabilized substituted aminomethane-1, 1-diphosphonic acid n-oxides and
use thereof in preventing scale and corrosion
Abstract
This invention relates to novel organic phosphonate compounds which can be
used as water treatment agents. More specifically, this invention relates
to 1,1 -diphosphonic acid N-oxides and water-soluble salts thereof for
control of corrosion and scale in aqueous systems. Preferred N-oxides are
morpholinomethane-1,1-diphosphonic acid N-oxide and
N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide.
Inventors:
|
Tang; Jiansheng (Sudbury, MA);
Kamrath; Michael A. (Aurora, IL)
|
Assignee:
|
Nalco Chemical Company (Naperville, IL)
|
Appl. No.:
|
186592 |
Filed:
|
November 5, 1998 |
Current U.S. Class: |
210/700; 210/764; 252/180; 252/389.22; 422/15; 562/13 |
Intern'l Class: |
C02F 005/14 |
Field of Search: |
210/699,700,764
252/180,389.21,389.22
422/15
562/12-14
|
References Cited
U.S. Patent Documents
3470243 | Sep., 1969 | Crutchfield et al. | 260/502.
|
3617576 | Nov., 1971 | Kerst | 210/699.
|
3957160 | May., 1976 | Ploger et al. | 210/700.
|
3979385 | Sep., 1976 | Wollmann et al. | 260/247.
|
4088678 | May., 1978 | Matt et al. | 210/699.
|
4246103 | Jan., 1981 | Block et al. | 210/699.
|
4892679 | Jan., 1990 | Blum et al. | 562/21.
|
4973744 | Nov., 1990 | Hwa et al. | 562/12.
|
5051532 | Sep., 1991 | Hwa et al. | 562/12.
|
5093005 | Mar., 1992 | Greaves | 210/700.
|
5096595 | Mar., 1992 | Hwa et al. | 210/700.
|
5167866 | Dec., 1992 | Hwa et al. | 210/700.
|
5259974 | Nov., 1993 | Chen et al. | 210/700.
|
5414112 | May., 1995 | Dragisich | 562/12.
|
5478476 | Dec., 1995 | Dragisich | 210/700.
|
5772893 | Jun., 1998 | Reed et al. | 210/699.
|
5788857 | Aug., 1998 | Yang et al. | 210/700.
|
Other References
NACE Corrosion/93, paper No. 266 (1993), "A Vovel Non-Heavy Metal Cooling
Water Treatment Effective Under Stagnant or Low Flow Conditions", D.
Hartwick, J. Chalut and V. Jovancicevic.
NACE Corrosion/94, paper No. 517 (1994), "Characterization of Pitting
Corrosion on Refinery Heat Exchangers", D. Hartwick, J. Richardson, V.
Jovancicevic and M. Peters.
|
Primary Examiner: Hruskoci; Peter A.
Attorney, Agent or Firm: Martin; Michael B., Breininger; Thomas M.
Claims
What is claimed is:
1. A method for preventing scale formation on metal surfaces in contact
with scale-forming industrial water within an industrial system which
comprises the step of treating said water with an effective
scale-inhibiting amount of a water-soluble calcium tolerated and biocide
stable 1,1-diphosphonic acid N-oxide selected from the group consisting
of:
compounds of formula (I)
##STR11##
wherein R.sup.1 and R.sup.2 are selected from the group consisting of:
straight chained alkyl groups, branched alkyl groups, alcohols, ethers,
thioethers, amines, esters, amides and carboxylic acids, R.sup.3 is
selected from the group consisting of hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (II):
##STR12##
wherein circle A represents a nitrogen-containing heterocycle, R.sub.3 is
selected from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (III):
##STR13##
wherein n is an integer of from 1 to about 8, R.sup.4 and R.sup.5 are
C.sub.1 -C.sub.6 alkyl groups, and M is selected from the group consisting
of hydrogen, alkaline metal ions, alkaline earth metal ions, ammonium
salts, zinc salts and aluminum salts,
and compounds of formula (IV):
##STR14##
wherein n is an integer of from about 1 to about 8, R.sup.3 is selected
from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl groups,
R.sup.4 is a C.sub.1 -C.sub.6 alkyl group and M is selected from the group
consisting of hydrogen, alkaline metal ions, alkaline earth metal ions,
ammonium salts, zinc salts and aluminum salts.
2. The method of claim 1 wherein said industrial system is a cooling water
tower and said industrial water is cooling water.
3. The method of claim 2 wherein said cooling water contains a biocide.
4. The method of claim 1 wherein said scale is calcium carbonate.
5. The method of claim 1 wherein said N-oxide of formula II is
morpholinomethane-1,1-diphosphonic acid N-oxide and its water soluble
salts.
6. The method of claim 1 wherein said N-oxide of formula I is
N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide and its
water-soluble salts.
7. A method for preventing corrosion on metal surfaces in contact with
corrosive industrial water within an industrial system which comprises the
step of treating said water with an effective corrosion inhibiting amount
of a water-soluble calcium tolerant and biocide stable 1,1-diphosphonic
acid N-oxide selected from the group consisting of:
compounds of formula (I):
##STR15##
wherein R.sup.1 and R.sup.2 are selected from the group consisting of:
straight chained alkyl groups, branched alkyl groups, alcohols, ethers,
thioethers, amines, esters, amides and carboxylic acids, R.sup.3 is
selected from the group consisting of hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (II):
##STR16##
wherein circle A represents a nitrogen-containing heterocycle, R.sub.3 is
selected from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (III):
##STR17##
wherein N is an integer of from 1 to about 8, R.sup.4 and R.sup.5 are
C.sub.1 -C.sub.6 alkyl groups, and M is selected from the group consisting
of hydrogen, alkaline metal ions, alkaline earth metal ions, ammonium
salts, zinc salts and aluminum salts, and
compounds of formula (IV):
##STR18##
wherein n is an integer of from about 1 to about 8, R.sup.3 is selected
from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl groups,
R.sup.4 is a C.sub.1 -C.sub.6 alkyl group and M is selected from the group
consisting of hydrogen, alkaline metal ions, alkaline earth metal ions,
ammonium salts, zinc salts and aluminum salts.
8. The method of claim 7 wherein the industrial system is a cooling water
tower.
9. The method of claim 7 wherein said N-oxide of formula II is
morpholinomethane-1,1-diphosphonic acid N-oxide and its water-soluble
salts.
10. The method of claim 7 wherein said N-oxide of formula I is
N,N-dimethylaminomethane-1,l-diphosphonic acid N-oxide and its
water-soluble salts.
11. A method for preventing scale formation on metal surfaces in contact
with sale-forming industrial water within an industrial system which
comprises the step of treating said water with an effective
scale-inhibiting amount of a water-soluble 1,1-diphosphonic acid N-oxide
selected from the group consisting of:
morpholinomethane-1,1-diphosphonic acid N-oxide and its water soluble salts
and N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide and its
water-soluble salts.
12. A method of preventing corrosion on metal surfaces in contact with
corrosive industrial water within an industrial system comprising adding
to the water with an effective corrosion-inhibiting amount of a
water-soluble 1,1-diphosphonic acid N-oxide selected from the group
consisting of:
morpholinomethane-1,1-diphosphonic acid N-oxide and its water soluble salts
and N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide and its
water-soluble salts.
Description
FIELD OF THE INVENTION
This invention relates to novel organic phosphonate compounds which can be
used as water treatment agents. More specifically, this invention relates
to 1,1-diphosphonic acid N-oxides and water-soluble salts thereof for
control of corrosion and scale in aqueous systems. Preferred N-oxides are
morpholinomethane-1,1-diphosphonic acid N-oxide and
N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide.
BACKGROUND OF THE INVENTION
Many industrial waters tend to be corrosive. Such waters, when in contact
with a variety of metal surfaces such as ferrous metals, aluminum, copper
and its alloys, tend to corrode one or more of such metals or alloys.
Ferrous metals such as carbon steel are among the most commonly used
structural materials in industrial systems. It is generally known that in
industrial systems having a ferrous metal in contact with an aqueous
solution, corrosion (both general and localized corrosion) of the metal is
one of the major problems. Loss of the metals from surfaces resulting from
general corrosion causes deterioration of the structural integrity of the
system or structure because of reduction of mechanical strength. It can
also cause problems such as underdeposit corrosion, increased heat
transfer resistance, or even blockage of the flow lines in other parts of
the system due to the transport and accumulation of corrosion products in
areas with low flow rates or geometric limitations. Localized corrosion
(e.g., pitting ) may pose an even greater threat to the normal operation
of the system than general corrosion because such corrosion will occur
intensely in one particular location and may cause perforations in the
system structure carrying an industrial water stream. Obviously, these
perforations may cause leaks which require shutdown of the entire
industrial system so that repair can be made. Indeed, corrosion problems
usually result in immense maintenance costs, as well as costs incurred as
a result of equipment failure. Therefore, the inhibition of metal
corrosion in industrial water is critical.
Corrosion protection of ferrous metals in industrial water systems is often
achieved by adding a corrosion inhibitor. Many corrosion inhibitors,
including chromate, molybdate, zinc, nitrite, orthophosphate, and
polyphosphate have been used previously, alone or in combination, in
various chemical treatment formulations. However, these inorganic
chemicals are either toxic and detrimental to the environment, or are not
very effective against localized corrosion, especially at economically
feasible and/or environmentally acceptable low dosage levels, although
they can usually provide satisfactory protection against general corrosion
(e.g., corrosion rate .ltoreq.3 mpy). Some organic phosphonates, such as
2-phosphonobutane-1,2,4-tricarboxylic acid (PBTC),
1-hydroxyethylidene-1,1-diphosphonic acid (HEDP) and
aminotrimethylenephosphonic acid (AMP) have been used previously as
corrosion inhibitors, alone or in combination with other corrosion
inhibitors, in various chemical treatment formulations. However, the
effectiveness of these phosphonate based treatments is generally
significantly lower than the treatments based on inorganic inhibitors.
U.S. Pat. No. 5,167,866 discloses that certain phosphonomethyl amine oxides
can be used as scale and corrosion inhibitors in aqueous systems. In
subsequent publications [D. Hartwick, J. Chalut and V. Jovancicevic,
Corrosion/93, paper no. 266, NACE, (1993); D. Hartwick, J. Richardson, V.
Jovancicevic and M. Peters, Corrosion/94, paper no. 517, NACE, (1994)],
ethanolamine bisphosphonomethyl N-oxide (EBO) was further identified to be
a particularly effective pitting inhibitor. Nevertheless, the
concentrations needed to obtain sufficient inhibition still appear to be
prohibitively high (e.g., >50mg/l EBO is needed to obtain an anodic
inhibition efficiency of greater than 40%).
Scale build-up is another serious problem in industrial water systems. The
build-up of deposit (scales) interferes with heat transfer, e.g., from the
inside surface of a heat exchanger tube (i.e.- the process side) to the
cooling medium such as water. The reduction of the rate of heat transfer
occurs because the scales formed generally have a lower heat transfer
coefficient than the metal tube itself. Thus, scaling reduces the
efficiency of the system. Further, scaling and deposits can lead to
corrosion underneath the deposits on the metallic surface and reduce the
useful life of the equipment. Calcium carbonate or sulfate as well as iron
oxides and hydroxides generated in the corrosion process are some of the
most commonly observed scale formers in industrial water systems.
The utilization of water which contains certain inorganic impurities, and
the production and processing of crude oil/water mixtures containing such
impurities, is plagued by the precipitation of these impurities with
subsequent scale formation. In the case of water which contains these
contaminants, the harmful effects of scale formation are generally
confined to the reduction of the capacity or bore of receptacles and
conduits employed to store and convey the contaminated water. In the case
of conduits, the impedance of flow is an obvious consequence. However, a
number of equally consequential problems are realized in specific
utilizations of contaminated water. For example, scale formed upon the
surfaces of storage vessels and conveying lines for process water may
break loose and these large masses of deposit can be entrained in and
conveyed by the process water to damage and clog equipment through which
the water is passed, e.g., tubes, valves, filters and screens. In
addition, these crystalline deposits may appear in, and detract from, the
final product which is derived from the process, e.g., paper formed from
an aqueous suspension of pulp. Furthermore, when the contaminated water is
involved in a heat exchange process, as either the "hot" or "cold" medium,
scale will be formed upon the heat exchange surfaces which are contacted
by the water. Such scale formation forms an insulating or thermal
pacifying barrier which impairs heat transfer efficiency as well as
impeding flow through the system.
Most industrial waters contain alkaline earth metal cations, such as
calcium, barium, magnesium, etc. and several anions such as bicarbonate,
carbonate, sulfate, oxalate, phosphate, silicate, fluoride, etc. When
combinations of these anions and cations are present in concentrations
which exceed the solubility of their reaction products, precipitates form
until these product solubility concentrations are no longer exceeded. For
example, when the concentrations of calcium ion and carbonate ion exceed
the solubility of the calcium carbonate reaction products, a solid phase
of calcium carbonate will form. Calcium carbonate is the most common form
of scale.
Solubility product concentrations are exceeded for various reasons, such as
partial evaporation of the water phase, change in pH, pressure or
temperature, and the introduction of additional ions which form insoluble
compounds with the ions already present in the solution.
As these reaction products precipitate on surfaces of the water carrying
system, they form scale or deposits. This accumulation prevents effective
heat transfer, interferes with fluid flow, facilitates corrosive processes
and harbors bacteria. This scale is an expensive problem in many
industrial water systems causing delays and shutdowns for cleaning and
removal.
Scale deposits are generated and extended principally by means of crystal
growth; and various approaches to reducing scale development have
accordingly included inhibition of crystal growth, modification of crystal
growth and dispersion of the scale-forming minerals.
While calcium sulfate and calcium carbonate are primary contributors to
scale formation, other salts of alkaline-earth metals and the aluminum
silicates are also offenders, e.g., magnesium carbonate, barium sulfate,
and the aluminum silicates provided by silts of the bentonitic, illitic,
and kaolinitic types among others.
Numerous compounds have been added to these industrial waters in an attempt
to prevent or reduce scale and corrosion, such as low molecular weight
poly(acrylic acid) polymers. Another class of compounds are the well known
organophosphonates which are illustrated by the compounds
hydroxyethylidene diphosphonic acid (HEDP) and phosphonobutane
tricarboxylic acid (PBTC). Another group of active scale and corrosion
inhibitors are the monosodium phosphinico(bis) succinic acids which are
described in U.S. Pat. No. 4,088,678.
Many organophosphorus compounds have been disclosed as scale inhibitors.
For example, N,N-bis (phosphonomethyl)-2-amino-1-propanol and derivatives
are disclosed in U.S. Pat. No. 5,259,974; ether diphosphonates are
disclosed in U.S. Pat. No. 5,772,893; N-substituted
aminoalkane-1,1-diphosphonic acids are disclosed in U.S. Pat. No.
3,957,160; and propane-1,3-disphosphonic acids are disclosed in U.S. Pat.
No. 4,246,103. Further, N-bis(phosphonomethyl) amino acids for the
prevention of calcium carbonate scale are disclosed in U.S. Pat. Nos.
5,414,112 and 5,478,476. 1,1-diphosphonic acid compounds are disclosed in
U.S. Pat. Nos. 3,617,576 and 4,892,679.
Hydroxyimino alkylene phosphonic acids are disclosed in U.S. Pat. No.
5,788,857. Furthermore, there are several references to the use of
N,N-bis-phosphonomethyl N-oxides such as the ethoxylated
N,N-bis-phosphonomethyl 2-(hydroxy)ethylamine N-oxides in U.S. Pat. No.
4,973,744; N,N-bis(phosphonomethyl)-2-amino-1-propanol N-oxide in U.S.
Pat. No. 5,259,974; oxidized tertiary amines in U.S. Pat. Nos. 5,096,595
and 5,167,866; N,N-bis-phosphonomethyl taurine N-oxide in U.S. Pat. No.
5,051,532; and tetrakis(dihydrogen phosphonomethyl)ethylene diamine
N,N-dioxides in U.S. Pat. No. 3,470,243. However, these compounds are
structurally different from those 1,1-diphosphonic acid N-oxides described
herein, in that these compounds are 1,3-diphosphonic acid 2-N-oxides,
while the compounds of the instant invention are 1,1-diphosphonic
acid-1-N-oxides. As will be seen from examples which follow, these
structural differences lead to superior anti-scale and anti-corrosion
characteristics.
Apparently, there is a need for a corrosion inhibitor that can effectively
prevent both general corrosion and localized (e.g., pitting) corrosion of
ferrous metals and can also efficiently prevent scale formation on
metallic surfaces in contact with the waters of various systems, such as
industrial process waters.
Among the objectives of this invention are: to provide a family of
N-alkylene-1,1-diphosphonic acid-1-N-oxides that can effectively provide
inhibition of localized (pitting) corrosion of ferrous metals in contact
with such systems; to provide a family of N-alkylene-1,1-diphosphonic
acid-1-N-oxides that can efficiently reduce general corrosion of ferrous
metals in contact with such systems; to provide a family of
N-alkylene-1,1-diphosphonic acid-1-N-oxides that can efficiently prevent
scale formation on metallic surfaces in contact with such systems; to
provide a family of N-alkylene-1,1-diphosphonic acid-1-N-oxides that can
simultaneously prevent localized corrosion, general corrosion of ferrous
metals, and scale formation on metallic surfaces in such systems, and to
provide a family of N-alkylene-1,1-diphosphonic acid-1-N-oxides which are
biocide stable and calcium tolerant.
SUMMARY OF THE INVENTION
This invention relates to novel organic phosphonate compounds which can be
used as water treatment agents. More specifically, this invention relates
to 1,1-diphosphonic acid N-oxides and water-soluble salts thereof for
control of corrosion and scale in aqueous systems. Preferred N-oxides are
morpholinomethane-1,1-diphosphonic acid N-oxide and
N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide.
DESCRIPTION OF THE INVENTION
The Phosphonic Acid N-Oxides
The following general formulae represent useful N-oxides for the practice
of this invention: general formula I:
##STR1##
general formula II:
##STR2##
general formula III:
##STR3##
and general formula IV:
##STR4##
Examples of compounds represented by formula I include the following and
their water-soluble salts:
##STR5##
The N-oxide of formula I may be N,N-dimethylaminomethane-1,1-diphosphonic
acid N-oxide and its water-soluble salts.
Examples of compounds represented by formula II include the following, and
their water-soluble salts:
##STR6##
R.sup.6 may be defined as a straight chain alkyl group, branched chain
alkyl group, alcohol, ether, thioether, amine, ester, amide or carboxylic
acid.
The N-oxide of formula II may be morpholinomethane-1,1-diphosphonic acid
N-oxide and its water soluble salts.
Among the suitable nitrogen heterocycles are pyrrolidine, piperidine,
quinuclidine, 1-azabicyclo [2,2,1]heptane and substituted derivatives
thereof.
One aspect of the invention is a method for preventing scale formation on
metal surfaces in contact with scale-forming industrial water within an
industrial system which comprises the step of treating said water with an
effective scale-inhibiting amount of a water-soluble 1,1-diphosphonic acid
N-oxide selected from the group consisting of:
compounds of formula (I):
##STR7##
wherein R.sup.1 and R.sup.2 are selected from the group consisting of:
straight chained alkyl groups, branched alkyl groups, alcohols, ethers,
thioethers, amines, esters, amides and carboxylic acids, R.sup.3 is
selected from the group consisting of hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (II):
##STR8##
wherein circle A represents a nitrogen-containing heterocycle, R.sub.3 is
selected from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl
groups, and M is selected from the group consisting of hydrogen, alkaline
metal ions, alkaline earth metal ions, ammonium salts, zinc salts and
aluminum salts,
compounds of formula (III):
##STR9##
wherein n is an integer of from 1 to about 8, R.sup.4 and R.sup.5 are
C.sub.1 -C.sub.6 alkyl groups, and M is selected from the group consisting
of hydrogen, alkaline metal ions, alkaline earth metal ions, ammonium
salts, zinc salts and aluminum salts,
and compounds of formula (IV):
##STR10##
wherein n is an integer of from about 1 to about 8, R.sup.3 is selected
from the group consisting of: hydrogen and C.sub.1 -C.sub.6 alkyl groups,
R.sup.4 is a C.sub.1 -C.sub.6 alkyl group and M is selected from the group
consisting of hydrogen, alkaline metal ions, alkaline earth metal ions,
ammonium salts, zinc salts and aluminum salts.
Another aspect of the invention is a method for corrosion control using the
above-described compounds.
An example of compounds represented by general formula III include those of
general formula III wherein R.sup.4 and R.sup.5 are methyl groups, and n
is 2.
An example of compounds represented by general formula IV include those of
general formula IV wherein R.sup.3 is hydrogen, R.sup.4 is a methyl group
and n is 2.
The Method
The phosphonic acid N-oxides described above are particularly advantageous
for the control of the deposition of calcium carbonate scale in cooling
water systems, especially for highly stressed cooling water systems such
as high temperature and high hardness cooling water systems. The
threshhold effect is exhibited whereby the formation of scale-forming salt
crystals and adherence to heat transfer surfaces is exhibited at low
treatment levels.
The precise dosage of N-oxide or salt suitable for controlling scale and
corrosion depends, to some extent, on the nature of the aqueous system to
be treated. A typical concentration range is from about 0.05 to about
10,000 ppm, with a preferred N-oxide concentration in amounts of from 0.1
to 500 ppm. More preferably from about 0.2 to about 100 ppm may be
utilized. Most preferably, from about 0.2 to about 20 ppm may be utilized.
Moreover, the phosphonic acid N-oxides can be used in combination with
other ferrous metal corrosion inhibitors, yellow metal corrosion
inhibitors, scale inhibitors, dispersants, biocides and additives. Such
combinations may exert synergistic effects in terms of corrosion
inhibitors, scale inhibition, dispersancy and bacterium control.
Examples of other corrosion inhibitors which can be used in combination
with the N-oxides are phosphorus-containing inorganic chemicals such as
orthophosphates, pyrophosphates, polyphosphates; hydroxycarboxylic acids
and their salts, such as gluconic, citric and tartaric acids; inorganic
ions such as Zn.sup.+2, Ce.sup.+2, MoO.sub.6.sup.2-, NO.sub.3.sup.- and
NO.sub.2- ; dibasic acids such as succinic and glutaric acid; nitrites;
and phosphonates such as N,N-bis(methylene phosphonic acids) like EBO, as
well as HEDP and PBTC.
Examples of the yellow metal corrosion inhibitors which can be used in
combination with the N-oxides include benzotriazole, tolyltriazole,
mercaptobenzothiazole and other azole compounds. Examples of other scale
inhibitors include polyacrylates, polymethacrylates, copolymers of acrylic
acid and methacrylate, copolymers of acrylic acid and acrylamide,
poly(maleic acid), copolymers of acrylic acid and maleic acid, polyesters,
poly(aspartic acid), functionalized poly(aspartic acid), terpolymers from
acrylic acid or acrylamide, sulfomethylated acrylamide copolymers,
HEDP(1-hydroxyethylidene-1,1-diphosphonic acid), PBTC
(2-phosphonobutane-1,2,4-tricarboxylic acid), AMP(amino tri(methylene
phosphonic acid), N,N-bis(methylene phosphonic acids) and mixtures
thereof.
Examples of biocides which can be used in combination with the N-oxides
include oxidizing biocides such as Cl.sub.2, NaOCl, Br.sub.2, NaOBr or
non-oxidizing biocides such as glutaraldehyde, isothiazolines
(5-chloro-2-methyl-4-isothiazoline-5-one and
2-methyl-4-isothiazoline-3-one), sulfamic acid stabilized bleach and
sulfamic acid stabilized bromine.
To treat a cooling water system, the compounds may be added to the cooling
tower basin or at any other location wherein good mixing can be achieved
in a short time. If oxidizing biocides are to be added in conjunction with
the N-oxides, addition points for these two components should be well
separated to avoid chemical interactions. In all other cases, order of
addition is inconsequential. The N-oxide may be added to the system at any
convenient point. Moreover, the necessary amount of N-oxide may be added
either periodically or continuously to the make-up water.
The term system as utilized herein is defined as any industrial process
which utilizes water. The system could contain primarily aqueous fluids,
or primarily non-aqueous fluids which also include water. Such systems are
found as industrial processes which utilize boilers or cooling water
towers. For example, the food processing industry is an industry which
requires such a system.
The industrial process water may be cooling water. The scale may be calcium
carbonate. Moreover, the scale may be derived from various system waters
containing calcium sulfate, calcium phosphate, calcium silicate, magnesium
carbonate, magnesium silicate, magnesium phosphate, barium carbonate,
barium sulfate, barium silicate, barium phosphate and iron oxide.
Additionally, the cooling water may contain a biocide.
Typical metal surfaces in cooling water systems which may be subjected to
corrosion or scale deposition are made of stainless steel, mild steel and
copper alloys such as brass among others.
The phosphonic acid N-oxides described above may be useful against scales
in such diverse systems as oilfields and petroleum refineries, pulp and
paper, and mining. These compounds may also have utility for iron clean
up, as metal sequestering or chelating agents and as dispersants for
clays.
The following examples are presented to describe preferred embodiments and
utilities of the invention and are not meant to limit the invention unless
otherwise stated in the claims appended hereto.
EXAMPLE 1
Diphosphonic acid starting materials were synthesized according to the
general procedure described in U.S. Pat. No. 3,979,385. To 29.81 grams of
N,N-dimethylaminomethane-1,1-diphosphonic acid (DMAMDP) in 25.0 grams of
deionized water was added 34 grams of 50% NaOH. This resulted in a
solution pH 9.7. Under cooling, hydrogen peroxide 19.28 grams (30%) was
added. The solution was heated at 60.degree. C. for 3 hours to afford a
clear solution. .sup.31 P NMR and .sup.31 C NMR analyses indicated that
all N,N-dimethylaminomethane-1,1-diphosphonic acid was converted into
N,N-dimethylaminomethane-1,1-diphosphonic acid N-oxide (DMAMDPO).
EXAMPLE 2
To 6.00 grams of N-morpholinomethane-1,1-diphosphonic acid (MMDP) was added
12.0 grams of deionized water and 7.2 grams of 50% NaOH. This resulted a
solution of pH 11.7. 10.42 grams of 30% hydrogen peroxide was added. The
solution was stirred overnight to afford a clear solution. .sup.31 P NMR
and .sup.3 c NMR analyses indicated that all
N-morpholinomethane-1,1-diphosphonic acid was converted into
N-morpholinomethane-1,1-diphosphonic acid N-oxide (MMDPO).
EXAMPLE 3
The following procedure was utilized to determine the calcium tolerance of
phosphono group containing compounds. Two solutions were made up. The
first was a 1000 mL of a 1000 ppm Ca solution (as CaCO.sub.3) which was
pH-adjusted to 9.0 by dropwise addition of dilute NaOH. The second was a
1000 ppm inhibitor solution also adjusted to pH 9.0 by dropwise addition
of dilute NaOH. Into a double-walled flask with recirculating water at
140.degree. F. was added 400 mls of the calcium solution. The inhibitor
solution was then added to the calcium containing solution, which was
magnetically stirred, at a rate of 1.0 mL/min with the solution
transmittance recorded at a wavelength of 420 nm. A plot of %
transmittance vs. inhibitor concentration gives a negative slope with the
magnitude being an indication of how inhibitor precipitation is occurring.
The ability of a potential calcium carbonate scale inhibitor to control
deposit formation is dependent on the inhibitor's availability during
scale formation. Inhibitor chemistries which are stable towards
precipitation at high calcium ion concentrations in the calcium tolerance
test have a wider application range than less calcium tolerant treatments.
As shown in Table I, the representative N-oxides MMDPO and DMAMDPO of the
instant invention display superior performance in calcium tolerance
testing, as the 100% transmittance indicates that there is no
precipitation at all.
TABLE I
______________________________________
Calcium Tolerance Comparison of Aminomethane-1,1-Diphosphonic
Acid N-Oxides to Conventional Treatments
Treatment % Transmittance.sup.5
______________________________________
None 100
PBTC.sup.1 94
HEDP.sup.2 85
MMDPO.sup.3 100
DMAMDPO.sup.4 100
______________________________________
.sup.1 = 2phosphonobutane-1,2,4-tricarboxylic acid
.sup.2 = 1hydroxyethane-1,1-diphosphonic acid
.sup.3 = morpholinomethane1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 2
.sup.4 = N,Ndimethylaminomethane-1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 1
.sup.5 = % transmittance after 100 ppm of inhibitor had been added.
Initial 1000 ppm calcium solution (as CaCO.sub.3) at pH 9.0 and
140.degree. F.
EXAMPLE 4
The constant composition technique was used to evaluate relative compound
effectiveness regarding crystal growth inhibition. This method uses seed
crystals which are introduced into a supersaturated solution of the seed
components and measures growth rates as titrants are consumed during the
crystallization process.
The procedure was performed as follows. A supersaturated solution of
calcium and carbonate was made in a double-walled glass cell with
recirculating water to maintain a constant temperature. The addition of
bicarbonate solution to the calcium solution was done slowly to insure
metastability. The ionic strength was then adjusted with NaCl and the pH
brought up to the desired value with dilute NaOH. Calcium carbonate seed
crystals were then added. Characterization of the seed by scanning
electron microscopy and triple point BET analysis indicated that the
particles were normal rhombohedrons and had a specific surface area of
0.38 m.sup.2 /gm.
As the experiment ran, calcium and carbonate/bicarbonate titrants were fed
to maintain a pH of 8.5. The titrant concentrations were chosen so that
the feed rate is not too fast or slow and are corrected for the subsequent
dilution of each by the other. The consumption of titrants was measured as
a function of time to obtain the growth rate. Inhibitor was typically
added after 5 mls of both titrants had been fed. Once the inhibitor is
depleted, the growth rate increases exponentially. The exponential growth
rate is extrapolated back to the x-axis, so that induction time can be
determined.
Data was analyzed by multiplying the induction time by a normalization
factor. This factor was obtained by dividing the slope observed just
before inhibitor addition by an average slope determined from six
replicate measurements. This operation compensated for different initial
growth rates which are very dependent upon specific seed surface area and
other environmental factors. The resulting data is a quantitative number
(normalized induction time) describing the relative ability of a
particular compound to inhibit crystal growth. Table II demonstrates that
the representative N-oxides perform as well as PBTC and HEDP, and better
than EBO and MOIPAMPO. However, as will be demonstrated by the next
Example, an advantage of the use of N-oxides over PBTC and HEDP (having
comparable inhibitory properties), is that the N-oxides are more stable in
the presence of biocides such as chlorides than the conventional
treatments.
TABLE II
______________________________________
Calcite Growth Inhibition for Aminomethane-1,1-Diphosphonic
Acid N-Oxides and an Amine bis-methylenephosphonic Acids
versus Conventional Treatments
Treatment Induction Time (min.).sup.8
______________________________________
None 0
PBTC.sup.1 550
HEDP.sup.2 650
EBO.sup.6 100
MOIPAMPO.sup.7
400
MMDPO.sup.3 570
DMAMDPO.sup.4 620
______________________________________
.sup.1 = 2phosphonobutane-1,2,4-tricarboxylic acid
.sup.2 = 1hydroxyethane-1,1-diphosphonic acid
.sup.3 = morpholinomethane1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 2
.sup.4 = N,Ndimethylaminomethane-1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 1
.sup.6 = hydroxyethyl bis(phosphonomethyl)amine Noxide
.sup.7 = methoxyisopropyl bis(phosphonomethyl)amine Noxide
.sup.8 = induction time is the time after seed addition and subsequent
inhibitor addition (5 mls titrant) until the intrinsic growth rate is
again observed, indicating inhibitor depletion
EXAMPLE 5
The stability of a potential inhibitor towards oxidation by biocides is an
important factor with regard to performance in an actual cooling tower
environment. In order to assess the relative stability of the phosphonic
acid N-oxides, degradation to inorganic phosphate was measured in the
presence of hypochlorite, as enumerated in Table III.
A synthetic water was made consisting of 400 ppm calcium, 200 ppm magnesium
and 400 ppm M alkalinity, all as CaCO.sub.3. The inhibitor was added at 25
ppm, as actives, prior to the bicarbonate to aid in preventing
precipitation. Sodium hypochlorite, as a 5.25% bleach solution, was then
added so that a nominal concentration of 40 ppm Cl.sub.2 was present. The
concentration was checked by a colorimetric method. Either the free
residual chlorine or inorganic phosphate concentration could then be
measured as a function of time to determine oxidation kinetics of the
inhibitor. A lower measured PO.sub.4 concentration indicates a greater
stability for the inhibitor under cooling tower conditions. MMDPO and
DMAMDPO do not degrade under these conditions, though the conventional
treatments do.
TABLE III
______________________________________
Chlorine Stability Comparison of Substituted
Aminomethane-1,1-Diphosphonic Acid N-oxides with
those of Substituted Aminomethane-1,1-Diphosphonic
Acids and Conventional Treatments
Treatment.sup.9
PO.sub.4 Concentration.sup.10
______________________________________
None 0
HEDP.sup.2 8
MMDP.sup.11 14
MMDPO.sup.3 0
DMAMDP.sup.12 15
DMAMDPO.sup.4 0
______________________________________
.sup.2 = 1hydroxyethane-1,1-diphosphonic acid
.sup.3 = morpholinomethane1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 2
.sup.4 = N,Ndimethylaminomethane-1,1-diphosphonic acid Noxide synthesized
according to the procedure of Example 1
.sup.9 = 25 ppm of inhibitor exposed to 40 ppm chlorine bleach (OCl, as
Cl.sub.2) after 25 hrs.
.sup.10 = inorganic PO.sub.4 measured by colorimetric method
.sup.11 = morpholinomethane1,1-diphosphonic acid
.sup.12 = N,Ndimethylaminomethane-1,1-diphosphonic acid
Changes can be made in the composition, operation and arrangement of the
method of the present invention described herein without departing from
the concept and scope of the invention as defmed in the following claims:
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